A visibility network of lines-of-sight connecting Iron Age sites in southern Spain, used to evaluate hypotheses of the role of lines of sight in facilitating visual control and communication during the later Iron Age in Southern Spain. It was used as a case study for evaluating the use of exponential random graph models (ERGMs) for visibility networks in this paper https://doi.org/10.1016/j.jas.2014.05.027
Construction
"A 35 m resolution DEM was created with the ‘Topo to Raster’ interpolation method in ArcGIS 9.3 (selected because it recreates a more correct representation of ridges from input point and contour data, features that have a significant impact on the results of visibility analyses), using point and contour line data (source: ICA, Junta de Andalucía; contour interval 10 m). Lines of sight were derived by performing a probable viewshed (Fisher, 1992, Fisher, 1995) with 100 iterations for each site. This allowed us to distinguish between lines of sight of high and low probability. A single observer point per site was used for the visibility analysis, since for the vast majority of sites there was no data available of the occupied area and extent of settlement. However, the decision to use a single observer location is problematic and its impact on the results will need to be evaluated in future work for smaller study areas with a better knowledge of occupied settlement areas. An observer height of 1.7 m was assumed. Moreover, we assumed that the observed location height is that of the DEM cell on which the observed settlement is located, since very few settlements have evidence of architectural features that could be included in the analysis.
The resulting visibility network (Fig. 6) was subsequently analysed using exploratory network measures, which revealed it consists of a number of components and three areas with a higher density of lines of sight (Brughmans et al., in press). The network used in the ERGMs includes lines of sight up to 20 km, at which distance fire and smoke signals are still visible, and with a probability higher than 50% (an arbitrary threshold, but a sensitivity analysis of network measures using different thresholds showed that it captures the key features of the network's structure (Brughmans et al., in press)). The final network, which will now be referred to as the “observed network” (prepared in the SNA software package UCINET), includes 159 nodes connected by 84 arcs."
Network creation description from https://doi.org/10.1016/j.jas.2014.05.027
point and contour line data from ICA, Junta de Andalucía; used to create DEM
site locations collected by the Urban Connectivity in Iron Age and Roman Southern Spain project directed by Simon Keay and Graeme Earl.
The sites dataset was primarily assembled from the following sources (text from https://doi.org/10.1007/s10816-014-9231-x):
"Archival: These are sites listed in regional site and monument catalogues held by the Delegacion Provincial de Cultura de la Junta de Andalucía (specifically the ARQUEOS and its later replacement the SIPHA). These draw upon information recorded by archaeologists in the 20th c., as well as works published earlier. The work of Ponsich (1974, 1979, 1987, 1991) form a fundamental part of this, particularly for the Roman settlements.
Administrative: These are specifically surveys of Iberian and Roman sites undertaken for administrative reasons by the Delegación Provincial de Cultura as part of the Junta de Andalucía’s ongoing strategy of updating its regional site and monument registers.
Research: These are sites that were found, investigated or excavated in the course of research projects undertaken by archaeologists based at the Universidad de Sevilla or elsewhere.
Accidental: These are sites found or investigated as a result of rescue work (‘urgencias’) undertaken by archaeologists on behalf of the Junta de Andalucía, whether by excavation or survey.
Project: These are sites visited in the course of the urban connectivity project for the purposes of checking location and analysis of surface materials for indications of chronology."